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Chemistry 2100 Lecture 10. Proteins Proteins serve many functions, including the following. Structure: –1. Structure: Collagen and keratin are the chief.

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Presentation on theme: "Chemistry 2100 Lecture 10. Proteins Proteins serve many functions, including the following. Structure: –1. Structure: Collagen and keratin are the chief."— Presentation transcript:

1 Chemistry 2100 Lecture 10

2 Proteins Proteins serve many functions, including the following. Structure: –1. Structure: Collagen and keratin are the chief constituents of skin, bone, hair, and nails. Catalysts: –2. Catalysts: Virtually all reactions in living systems are catalyzed by proteins called enzymes. Movement: –3. Movement: Muscles are made up of proteins called myosin and actin. Transport –4. Transport: Hemoglobin transports oxygen from the lungs to cells; other proteins transport molecules across cell membranes. Hormones: –5. Hormones: Many hormones are proteins, among them insulin, oxytocin, and human growth hormone.

3 Proteins Protection: –6. Protection: Blood clotting involves the protein fibrinogen; the body used proteins called antibodies to fight disease. Storage: –7. Storage: Casein in milk and ovalbumin in eggs store nutrients for newborn infants and birds. Ferritin, a protein in the liver, stores iron. Regulation: –8. Regulation: Certain proteins not only control the expression of genes, but also control when gene expression takes place. Proteins are divided into two types: –Fibrous proteins –Globular proteins

4 nonpolar polar / neutral acidic / basic

5 Chirality of -Amino Acids With the exception of glycine, all protein- derived amino acids have at least one stereocenter (the -carbon) and are chiral. –The vast majority of -amino acids have the L- configuration at the -carbon.

6 nonpolar polar / neutral acidic / basic

7 Protein-Derived -Amino Acids Nonpolar side chains (at pH 7.0)

8 Protein-Derived -Amino Acids Polar side chains (at pH 7.0)

9 Acidic and basic side chains (at pH 7.0) Protein-Derived -Amino Acids

10 essential amino acids Leu, Ile, Lys, Met, Phe, Thr, Trp, Val, His ( Arg, Tyr, Cys )

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12 Ionization vs. pH The net charge on an amino acid depends on the pH of the solution in which it is dissolved. –If we dissolve an amino acid in water, it is present in the aqueous solution as its zwitterion. –If we add a strong acid such as HCl to bring the pH of the solution to 0.0, the strong acid donates a proton to the -COO - of the amino acid turning the zwitterion into a positive ion.

13 Ionization vs. pH –If we add a strong base such as NaOH to the solution and bring its pH to 14, a proton is transferred from the NH 3 + group to the base turning the zwitterion into a negative ion. –To summarize:

14 Problem: Calculate the net charge of lysine at pH = 3, 7, 11. Estimate pI for lysine.

15 pH = 7

16 (–)

17 pH = 7 (–) (+)

18 pH = 7 (–) (+)

19 pH = 7 (–) (+)

20 pH = 3pH = 7 (–) (+)

21 pH = 3 (+) pH = 7 (–) (+)

22 pH = 11pH = 3pH = 7 (–) (+)

23 pH = 11pH = 3pH = 7 (–) (+) (–)

24 Isoelectric Point (pI) Isoelectric point, pI:Isoelectric point, pI: The pH at which the majority of molecules of a compound in solution have no net charge.

25 Problem: Predict the electrophoresis behavior at pH 6.0 of a mixture of alanine (pI 6.0), aspartic acid (pI 2.8) and lysine (pI 9.7)

26 Problem: Predict the electrophoresis behavior at pH 6.0 of a mixture of alanine (pI 6.0), aspartic acid (pI 2.8) and lysine (pI 9.7)

27 Problem: Predict the electrophoresis behavior at pH 6.0 of a mixture of alanine (pI 6.0), aspartic acid (pI 2.8) and lysine (pI 9.7)

28 Lys Ala Asp Problem: Predict the electrophoresis behavior at pH 6.0 of a mixture of alanine (pI 6.0), aspartic acid (pI 2.8) and lysine (pI 9.7)

29 Peptide Bonds

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39 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus ) (+)

40 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus ) (+)

41 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus ) (+)

42 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus ) (+)

43 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus ) (+)

44 pH = 7 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus )

45 pH = 7 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus ) (+)

46 pH = 3 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus ) (+)

47 pH = 3 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus ) (+)

48 pH = 11 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus )

49 pH = 11 lysylserylmethionylaspartylarginine [ Lys–Ser–Met–Asp–Arg ] (–) ( N-terminus ) ( C-terminus )

50 (5!) = 120 combinations (20!) = eicosapeptides (20 5 ) = possible pentapeptides

51 (5!) = 120 combinations (20!) = eicosapeptides (20 5 ) = possible pentapeptides

52 (5!) = 120 combinations (20!) = eicosapeptides (20 5 ) = possible pentapeptides

53 (5!) = 120 combinations (20!) = eicosapeptides (20 5 ) = possible pentapeptides

54 (5!) = 120 combinations (20!) = eicosapeptides (20 5 ) = possible pentapeptides

55 (5!) = 120 combinations (20!) = eicosapeptides (20 5 ) = possible pentapeptides

56 oxytocin vasopressin

57 Tyr–Gly–Gly–Phe–Met Methionine enkephalin Morphine Tyr–Gly–Gly–Phe–Leu Leucine enkephalin Enkephalins

58 SS Gly – Ile – Val – Glu – Gln – Cys – Cys – Thr – Ser – Ile – Cys – Ser – Leu – Tyr – Gln – Leu – Glu – Asn – Tyr – Cys – Asn Phe – Val – Asn – Gln – His – Leu – Cys – Gly – Ser – His – Leu – Val – Glu – Ala – Leu – Tyr – Leu – Val – Cys – Gly – Glu – Arg – Gly – Phe – Phe – Tyr – Thr – Pro – Lys – Thr S S S S Insulin

59 Structure of Proteins

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64 Secondary Structure: The -Helix

65 -Pleated Sheet

66 Random Coil

67 -helix -pleated sheet

68 Protein Tertiary Structure

69 -helix -pleated sheet

70 salt bridge -helix -pleated sheet

71 hydrogen bond salt bridge -helix -pleated sheet

72 hydrogen bond hydrogen bond salt bridge -helix -pleated sheet

73 hydrogen bond hydrogen bond salt bridge hydrophilic interaction to water -helix -pleated sheet

74 hydrophobic interaction hydrogen bond hydrogen bond salt bridge hydrophilic interaction to water -helix -pleated sheet

75 hydrophobic interaction hydrogen bond hydrogen bond salt bridge hydrophilic interaction to water -helix -pleated sheet

76 hydrophobic interaction disulfide bond hydrogen bond hydrogen bond salt bridge hydrophilic interaction to water -helix -pleated sheet

77 Protein Quaternary Structure

78 C 3032 H 4816 N 735 O 780 S 8 Fe 4 (MW 64,450) Hemoglobin

79 Sickle-Cell Anemia

80 Sequence Varies: Ask 23andMe

81 Proteins

82 Denaturation

83 Denaturation… also known as Cooking

84 Misfolding Diseases

85 Mutation Impairs Proper Folding Cystic Fibrosis Sickle Cell Anemia

86 Contagious Misfolding: Prions


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